1. Field of the Invention
The present invention relates to an apparatus for treating or processing semiconductor wafers and, more particularly to a semiconductor wafer-processing apparatus having a mechanism for transporting semiconductor wafers into and out of a plurality of processing units.
2. Description of the Related Art
An apparatus for heat-treating semiconductor wafers is known which comprises a plurality of horizontally extending heat-treatment furnaces arranged one above another, and a plurality of boat-inserting/extracting mechanism for inserting boats into the furnaces and extracting them from the furnaces. Semiconductor wafers mounted on each boat are moved into and pulled from the furnace as the boat is moved into and from the furnace by means of the corresponding boat-inserting/extracting mechanism.
Japanese Patent Publication No. 62-76897 discloses an apparatus for transporting boats to boat-inserting/extracting mechanisms. This boat-transporting apparatus includes a combination of an elevator mechanism and a horizontal trans-port mechanism having a boat holder. In operation, the elevator mechanism moves the horizontal transport mechanism up or down to a desired furnace. Then, the horizontal transport mechanism is driven, thereby horizontally moving the boat holder close to the opening of the furnace. Finally, the boat-transporting mechanism moves a boat into, and from, the heat-treatment furnace.
The conventional boat-transporting apparatus is disadvantageous in some respect. Both the elevator mechanism and the horizontal transport mechanism remain idle until the boat-transporting mechanism inserts the boat into the heat-treatment furnace so that the wafers mounted on the boat are heat-treated within the furnace. More precisely, the elevator mechanism and the horizontal transport mechanism cannot perform their functions while the boat is being moved to and into any heat-treatment furnace. Obviously, the operating efficiency of the boat-transporting apparatus is low since the elevator mechanism and the horizontal transport mechanism remain idle for a long time.
The boat-transporting apparatus is disadvantageous in another respect. The apparatus cannot simultaneously take the heat-treated wafers from two or more furnaces. Until the horizontal transport mechanism is moved to the furnace after the wafers have been pulled out of a furnace, the heat-treated wafers in any other furnace must remain in the furnace. Consequently, these wafers are heated for a time longer than necessary, or heated in excess, failing to have quality as high as desired.